1. Field of the Invention
The present invention relates to a high performance rain tyre which is provided with a tread pattern which is particularly configured to improve the grip of the tyre on wet road surfaces even under conditions of extreme maximum stress, as in the case of use in high-power vehicles and vehicles in motor sport competitions.
2. Description of the Related Art
In order to ensure adequate road holding even on a wet road surface, rain tyres have a tread band which is provided with grooves and notches of various formations and geometries, whose function is to allow the discharge of water present between the surface of the tyre and the road surface at the time of mutual contact, preventing the hydrostatic pressure resulting from the impact of the water against the advancing tyre from being able to cause even partial lifting of the tyre off the road surface and consequent loss of control of the vehicle. This phenomenon, known as aquaplaning, is closely correlated with the speed of the vehicle, so that consideration thereof becomes particularly critical when the tyre is used in vehicles capable of developing high speeds, such as high-powered sports cars or, to an even greater extent, in vehicles used in motor sport competitions.
Although the presence of grooves and notches in the tread on the one hand allows water to be discharged, on the other hand they necessarily reduce the contact surface of the tyre with the road surface, thereby limiting the grip capacity thereof when subjected to braking and acceleration, or when driving round bends.
Therefore, there is an evident need to provide a rain tyre which is provided with a tread pattern which allows the best possible balance to be obtained between the opposing demands set out above, optimizing the number, geometry and formation of grooves and notches.
In the context of the present description and of the appended claims, the following definitions are used.
The term “circumferential groove” is intended to refer to a groove which extends continuously along the entire circumference of the tread in a substantially parallel manner with the equatorial plane and which has a mean width greater than or equal to 8 mm and preferably of between approximately 8 mm and approximately 16 mm and a depth greater than or equal to 3 mm and preferably of between approximately 3 mm and approximately 10 mm.
The term “transverse groove” is intended to refer to a groove which extends, with any path, from a shoulder zone of the tyre towards an equatorial zone of the tyre. In greater detail, a transverse groove may follow any path and may include rectilinear portions with different inclinations and/or curves with variable curvature.
Furthermore, it is intended to be understood that a “groove extends continuously” when the axis thereof follows a continuous curve, that is to say, it does not have any points of discontinuity, with the further distinction that, in the event of intersection with other grooves or notches, the ideal extension of the axes of the two groove portions facing the intersection shall be considered.
It will further be understood that a “groove maintains a constant width” when the width of the groove measured in any cross-section thereof as the distance between the edges which delimit it remains within a range of 10% of a mean value of the width measured over the entire development of the groove. In order to establish that, there are excluded the lateral end zones of the transverse grooves defined in the last 30 mm of the development of the groove, so that in that lateral end zone, generally near the lateral edge of the tread band, the groove may have, for example, a tapered conformation with a progressively smaller width.
The term “subsidiary circumferential notch” is intended to refer to a notch which extends continuously along the entire circumference of the tread in a substantially parallel manner with the equatorial plane and which has a mean width and/or depth less than those indicated in the definition of circumferential groove.
The inclination of a groove portion with respect to an axial direction of the tyre is considered with reference to the acute angle formed by a development direction of that groove portion with the axial direction of the tyre, so that a first groove portion will be considered “greatly inclined with respect to an axial direction of the tyre” with respect to a second groove portion when the acute angle formed by the development direction of the first groove portion with the axial direction of the tyre is greater than the acute angle similarly formed by the development direction of the second groove portion.
However, in order to identify in an unambiguous manner the inclination of any direction defined on the tread of the tyre, there is identified the angle formed by that direction with a half-line lying in the equatorial plane, tangential to the tread and orientated in accordance with the travel direction of the tyre, considering the angles measured in a clockwise direction to be positive.
As a result, therefore, a groove portion becomes more inclined with respect to an axial direction of the tyre the more the angle formed by the development direction thereof with respect to the equatorial plane approaches 0° or ±180° whereas, on the other hand, it becomes less inclined with respect to an axial direction of the tyre the more the angle formed by the development direction thereof with respect to the equatorial plane approaches ±90°.
It may further be set out that the development direction of a groove portion which is necessary for defining the inclination angle thereof coincides with the axis thereof when the portion is substantially rectilinear whilst, when the axis is curved, it is defined by the straight line extending through the end points thereof.
Finally, the term “groove portion” is intended to refer to any groove portion extending over a measurement of more than 20 mm.
Another parameter used in the technical field being referred to for a quantitative evaluation of the presence of a groove in the tread pattern is the “sea-land ratio”, a dimensionless number defined as the ratio between the tread surface affected by grooves and notches, and therefore not in abutment with the road surface, and the total surface of the tread.
This parameter may be assessed both over the entire tread and at a specific portion thereof and, in some motor sports competitions such as, for example, Formula 1, is subject to precise regulatory arrangements which, in order to ensure an adequate level of safety for the drivers, set down a minimum value therefore.